Most image forming apparatuses, such as MFPs (Multi-Functional Peripherals), are equipped with multiple feed trays containing print sheets, and are configured to automatically change a feed tray to be used for printing, according to the amount of sheets loaded in each of the multiple feed trays, so as to prevent the processing of a print job from being interrupted because of an empty feed tray.
As one example of a technique to obtain the amount of sheets in a feed tray, Japanese Unexamined Patent Publication (JP-A) No. 2000-281243 discloses an image forming apparatus including a sheet tray that stores sheets for printing. The image forming apparatus is configured to feed sheets one by one from the sheet tray into a sheet conveyance path and form an image on each sheet conveyed to an image thrilling position in the sheet conveyance path. The image forming apparatus further includes a supplied-sheet counter that counts the number of sheets supplied into the sheet tray, a fed-sheet counter that counts the number of sheets fed into the sheet conveyance path from the sheet tray, and a remaining-sheet amount calculator that calculates the amount of remaining sheets in the sheet tray on the basis of a count result given by the supplied-Sheet counter and a count result given by the fed-sheet counter.
As one example of control of an image forming apparatus according to the amount of sheets in a feed tray, JP-A No. H09-081344 discloses a printing system that includes a printer and a host computer that sends print data to the printer to make the printer to execute printing. The printer includes a remaining-sheet sensor that senses the amount of remaining print sheets in a feed tray. The host computer includes a necessary-sheet amount calculator that calculates the amount of print sheets necessary for one printing process; and a determiner that determines whether there are enough print sheets by comparing the amount of necessary print sheets calculated by the necessary-sheet amount calculator and the amount of remaining print sheets given by the remaining-sheet sensor. The host computer further includes a notifier that notifies the shortage of print sheets when the determiner has determined there are not enough print sheets, and a control processor that, in response to receiving a notification of the shortage of print sheets from the notifier, controls the host computer so as to make the printer execute printing on condition that print sheets has been supplied into the feed tray.
As another example of the control, JP-A No. 2006-298652 discloses a sheet-feed control device for an image forming apparatus equipped with multiple feed trays. The sheet-feed control device includes a memory that memorizes the quality of sheets stored in each of the multiple feed trays; an alternative decider that, on finding a feed tray, which is a current sheet feeder among the multiple feed trays, in a state incapable of feeding sheets, decides a certain feed tray as an alternative sheet feeder, where the certain feed tray stores sheets the quality of which is different form the quality of sheets in the current sheet feeder and is specified in advance as an alternative to the quality of sheets in the current sheet feeder; and a changer that changes the sheet feeder to another feed tray on the basis of the decision of the alternative decider.
As another example of the control, JP-A No. 2007-065323 discloses an image forming apparatus including multiple sheet-storage units each storing sheets; a sheet feeder disposed in each of the multiple sheet-storage units so as to feed sheets out from the sheet-storage unit; and a control processor that changes the mode of changing sheet-feed operations from those using a certain sheet-storage unit to those using another sheet-storage unit automatically, between the first mode to change a sheet-storage unit to be used for the sheet-feed operations, from the sheet-storage unit currently being used to another sheet-storage unit, with a certain amount of sheets left in the sheet-storage unit currently being used, and the second mode to change a sheet-storage unit to be used for the sheet-feed operations, from the sheet-storage unit currently being used to another sheet-storage unit after all the sheets in the sheet-storage unit currently being used have been fed out.
In commercial printing, in order to stock a large volume of print sheets stably, printers or publishers implement redundancy of sheet suppliers, by getting print sheets from multiple sheet suppliers. Such print sheets can have some differences in terms of texture and paper color depending on the manufacturer, even if the print sheets are manufactured according to similar specifications, and need to be handled with being loaded in separate feed trays according to the differences.
However, the conventional techniques of automatically changing a feed tray, select a feed tray to be used for printing, on the basis of just the amount of sheets in each feed tray. Therefore, when the currently-used feed tray becomes empty (or the amount of sheets in the currently-used feed tray becomes equal to or less than a predetermined amount), the conventional techniques automatically change a feed tray being used for printing to another feed tray even in the middle of printing one print product irrespective of the processing state of a print job. In an image forming apparatus equipped with multiple feed trays for sheets of the same size, in which sheets of different kinds are loaded, the conventional techniques can cause a problem such that the image forming apparatus can create print products having less commercial value to be used for commercial printing, for example, a document including two facing pages printed on sheets different in texture and/or paper color.